Combustion pressure feedback based engine control with variable resolution sampling windows

ABSTRACT

A system for controlling an internal combustion engine has an in-cylinder pressure sensor, a crank angle sensor and a controller coupled to receive inputs from the pressure sensor and crank angle sensor. The controller is configured to convert the cylinder pressure input into a combustion metric indicative of the combustion occurring in the measured cylinder and control fuel input and timing into the engine based on the combustion metric. The controller samples the in-cylinder pressure sensor at a high frequency during critical combustion events and at a lower frequency during the non-critical cylinder conditions.

CLAIM OF PRIORITY

This application claims priority under 35 USC § 120, and is a Divisionalapplication to U.S. patent application Ser. No. 15/099,486 filed Apr.14, 2016; which claims priority under 35 USC § 119(e) to U.S. PatentApplication Ser. No. 62/147,405, filed on Apr. 14, 2015, both of whichand the entire contents of thereof are hereby incorporated by reference.

BACKGROUND

Combustion monitoring via cylinder pressure is used to develop enginecombustion strategies and their control on nearly all engines in theresearch and development environment. However, cylinder pressure basedmonitoring systems on production engines remain short on capability, andare expensive and unreliable, thus limiting their applicability to onlythe highest power density and highest efficiency applications wheretheir benefits can be justified against their cost.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of the engine control system.

FIG. 2 is a schematic flow diagram of the operation of the system.

FIG. 3 is a schematic of an engine control unit showing inputs, outputs,and set points.

FIG. 4 is a schematic of the internal processing steps of the enginecontrol unit of FIG. 3.

FIG. 5 is a graph of pressure vs. crank angle for a cylinder showingthree pressure sampling rate windows.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The concepts herein encompass controlling an engine using high-frequencyin-cylinder pressure measurements processed by an engine control unit(ECU) at varying sampling rates, wherein the sampling rate is based onwhere the cylinder is in the combustion cycle. The concepts disclosedherein provide an ability to operate based on in-cylinder pressuremeasurements without the need for a high power processor, and in certaininstances, without requiring a separate higher power ECU for processingthe pressure signals to combustion metrics that resides apart from theECU for determining and controlling the ignition timing and fueling. Thevariable sampling rates can reduce memory and computation demand on theECU by reducing the rate of calculation of combustion metrics duringless operationally significant regions of engine operation. Usingin-cylinder pressure measurements can eliminate the need for usingmultiple other sensors for engine control, for example, eliminating theneed for a mass-air-flow sensor, NOx (oxides of nitrogen) sensor, knocksensor or exhaust temperature sensor. Moreover, in certain instances,the concepts herein enable better adapting to variations in fuel quality(e.g., variations in methane number (MN) and energy content (MBTU/m³).

The engine control unit (ECU) has an embedded processor with, in certaininstances, the capability to process high-speed cylinder pressure datawith resolution as fine as 0.25° crank and capable of producing acomprehensive suite of diagnostics for monitoring combustion, as wellas, filtering and averaging the combustion diagnostics in real-time,i.e., concurrent with the engine operation and current enough for use ina control loop for controlling the engine. In some instances, the ECU iscapable of processing up to 20 cylinders in real-time with the totalprocessing time for each cylinder of around 2.5 milliseconds. Thereal-time combustion metrics calculated by the ECU can include location,in crank angle or time, of peak pressure (P_(loc)) and maximum pressure(P_(max)) within one or more the cylinders. Additionally, in certaininstances, the ECU can calculate, on a cylinder-by-cylinder basis, theadiabatic heat release rate of the per cycle combustion, the locations,in crank angle or time, of 10%, 50%, 90% of the per cycle combustion(CA10, CA50 (AKA Center of Combustion (CoC)), and CA90) and the durationof 10-90% of per cycle combustion, as well as other combustiondiagnostics metrics derived from the pressure signal, such as IMEP(indicated mean effective pressure, polytropic coefficients (K,indicative of compression quality of the cylinder), combustion stability(COV of IMEP).

Examples of the embedded pressure monitoring system can be found inclosed-loop control on a modern four-cylinder, reciprocating dieselengine, in both a conventional dual-fuel natural gas-diesel mode, and aReactive Controlled Compression Ignition, or RCCI, gas-diesel mode—in aresearch lab environment. However, the concepts are not limited and areapplicable to any other engine configurations such with fewer or morecylinders, different fuel types, and to other, non-reciprocating typesof engines. And concepts disclosed herein go beyond the research labenvironment to be made practical in an embedded ECU.

For a gas-diesel dual-fuel operation, control to a constant CA50 (crankangle at 50% of combustion heat release) is demonstrated for a varyingset point as well as for rejection of external disturbances, such as EGRand fuel injection pressure. For RCCI mode, closed-loop control of CA50is demonstrated.

In some instances, the concepts herein encompass natural gas enginesthat employ cylinder pressure monitoring to determine the IMEP andcenter of combustion (CA50) as primary methods based upon newcapabilities, such as heat release, herein disclosed, while also beingable to monitor and control on more conventional pressure only methodssuch as the magnitude and location of peak pressure and adjust spark andfueling to balance the cylinders, while safely keeping the peak pressurebelow the engine design limits. According to the concepts herein, insome diesel engines, ignition delay can be monitored to enable real-timeinjector re-calibration. According to the concepts herein, in somenatural gas-diesel dual-fuel engines, a pressure monitoring systemenables the substitution rate of gas-to-diesel to be maximized bymonitoring combustion phasing and knock, and then compensating with gasinjection rates and diesel injection timing to maintain maximumsubstitution rates without knock.

For Homogeneous Charge Compression Ignition (HCCI), Premixed ChargeCompression Ignition (PCCI), and RCCI and other low temperaturecombustion (LTC) modes, combustion feedback can be used to maintain keycombustion parameters within specified limits. Combustion parameterssuch as location of start of combustion (SOC), center of combustion(CA50), the rate of pressure rise (RPR), and maintaining P_(max) belowthe engine limit are provided to the controller.

Conventional methods which exist prior to this innovation include ECUsystem uses cylinder pressure monitoring fed directly into a controllerand using the pressure ratio method, such that the ECU then adaptsspark-timing control and dilution control, to balance cylinders andconduct misfire and knock detection. The innovation departs from theconventional method by processing the pressure trace and converting itinto multiple useful combustion metrics way beyond Peak Pressure onlymethods, by the high speed processor using efficient vectoring and thealgorithms which provide flexibility to wrap controls and diagnosticsaround the metrics, in contrast to the conventional method which onlyuses the voltage of the pressure sensor directly into a “one kind ofcontrol” controller.

The conventional ECU system, in some instances, due to memory andprocessor limitations, analysis of the pressure trace can be limited toinformation customized to work directly with the engine control strategyand the processor for determining the combustion metrics is embedded inthe same device as the remainder of the engine control unit. In a memoryor processor limited implementation, the conventional ECU system selectsonly a small subset of the combustion metrics and uses surrogateanalyses that are useful only for a one of a kind pre-designed enginecontrol objective; they are not general.

One of the objectives of the ECU system is to convert high-speedcylinder pressure data into meaningful low speed data that can informthe user of the engine operating conditions within a small number ofengine cycles—especially during calibration—and provide stable andreliable smart sensor input to the ECU to deliver the followingbenefits. In some instances, the ECU system enables engine protectionvia appropriate actuator changes to provide over-pressure protection(P_(max)), pressure rise rate protection (RPR), knock detection, andmisfire detection. In some instances, the ECU system calculatescombustion metrics in order to determine the above actuator changes(e.g. spark timing, in-cylinder injection and port injection timing andduration, AFR control, and throttle position. In some instances, thecalculated combustion metrics are optimal P_(loc), optimal CA50,resulting RHR, start of combustion (SOC), and indicated mean effectivepressure (IMEP) cylinder balancing.

In some instances, the system is built into an embedded controller thatcommunicates with the main controller directly or over a controller areanetwork (CAN) link, and without significant time lag. Alternatively, insome instances, the method is performed directly on the main processorof the ECU, assuming adequate computational power is available.

In some instances, the engine control device is configured to improveknock margin in gas engines, improve maximum gas-to-diesel substitutionrates in a gas diesel dual-fuel application, and enable precise controlof combustion phasing of an LTC strategy such as HCCI, RCCI, PCCI, allwithin the engine protection limits.

FIG. 1 is a schematic of the engine control system. FIG. 1 shows aschematic of the ECU 11 within the engine control system 10 configuredto control an engine 13. As indicated above, high-speed pressure data 14is generated by pressure sensors 4, each mounted with direct access tothe combustion chamber. The pressure signal 14 is captured at a highcrank-synchronous rate—as fine as 0.25° resolution or 2880 samples perengine cycle. This synthetic crank angle signal is generated from thelower resolution crank position signal. For example, with a typicalcrank angle encoder 5 generating a crank angle signal 15 by sensingpassage of the edge of teeth on a disk, the disk mounted to rotate withthe crank, the resolution of the crank position is based on the numberof teeth. A typical 60-2 tooth wheel has a resolution of 6°. However,interpolation can used to determine the crank angle in the space betweenof the edges. Thus, the spacing between edges uses the previouslyobserved tooth period divided by the number of edges required to achievethe desired angular sampling resolution. To account for minorvariability between the crank teeth that can be seen even when theaverage engine speed is constant, and the encoder system isre-synchronized on each edge.

The resulting high-resolution pressure signal 14 is used by thecombustion diagnostics routine in the ECU 11 to produce the keycombustion diagnostics 19 on a per-cylinder, per cycle basis, forexample, IMEP, P_(max), CA50. The metrics 18 are subsequently used bythe ECU 11 as a feedback signal for adjusting key combustion performancecharacteristics by modulating engine control actuator settings 19.

In conventional (non-LTC) dual-fuel operation, combustion phasing is acritical factor for efficiency, emissions, and knock margin. Goodcontrol of combustion phasing can significantly improve the maximum gassubstitution rate. As not all variables in the engine can be held totight tolerances (including manifold absolute temperature (MAT),manifold absolute pressure (MAP), and diesel injection rail pressure forexample), typical open-loop methods of controlling combustion phasingcan be significantly enhanced by some feedback mechanism.

Reactivity Controlled Compression Ignition (RCCI) is a one of many LTCstrategies to dramatically reduce NOx production and simultaneouslyachieve fast combustion of lean mixtures to improving efficiency. InRCCI, two fuels of different reactivity are introduced early into thecombustion chamber to adjust the phasing of combustion initiation andrate of combustion. In gas-diesel RCCI, natural gas is injected into theintake port and diesel is injected directly into the combustion chamber.With diesel common rail, it is possible to inject the diesel portion atvarious times and quantities up to the limitations of the injectionsystem. Typically, the diesel is injected much earlier than normaldiesel or gas-diesel dual-fuel as early as just after intake valveclosing (IVC) to as late as 70° before top dead center (BTDC, where TDCis the crank position at which the piston is in its top most positionwithin the cylinder). Additionally, the ‘gain’ switches sign, where inRCCI, earlier diesel timing leads to later combustion phasing—which isthe opposite of diesel and dual-fuel combustion where earlier dieselleads to earlier combustion phasing.

FIG. 2 shows an example flow diagram of the internal operation of theECU 12 of system 10. While shown as separate ECU coupled with a databus, in other instances, the ECU 12 can be a single ECU with a commonprocessor or separate processors for the combustion metric determinationand the engine control. FIG. 2 shows the ECU 12 accepting inputs from acrank angle sensor 201 and an in-cylinder pressure sensor 202. The crankangle sensor 201 need not be a high resolution sensor, and in certaininstances, it can be a sensor reading a 60-2 tooth wheel. For eachcylinder, the ECU 12 calculates combustion metrics from the input data201, 201. In the ECU 12, for each cylinder, the following steps areexecuted in a pressure sensor processing module 21. First, at step 211,all constants are defined, including vectors via engine geometry. Next,at step 212, the in-cylinder pressure is captured, in some instances, ata specified sampling rate defined by a sampling rate window. Next, atstep 213, the raw pressure data is parsed into vectors according to thecorresponding crank angle. Next, at step 214, combustion metrics arecalculated using predefined vectors and the pressure vector. Finally, atstep 215, the heat release rate and combustion durations (i.e., 10%,50%, and 90% burn) are calculated.

The results of the per-cylinder combustion metrics are fed to the enginecontrol module 22 of the ECU 12, where the following steps are executed.The engine control module 22 of FIG. 2 shows the manner of usingreal-time heat release calculations to operate a dual-fuel engine tomeet an IMEP, or similar, target. (FIG. 4 shows a similar embodiment fora single fuel gas engine—spark timing, throttle setting and fuel rate).First, at step 221, the optimum engine timing are determined via thereal-time heat release calculated at step 815. Next, at step 222, themulti or single pulse diesel timing are adjusted by the injector toachieve a phasing target. Next, at step 223, a target substitution rateis determined via the real-time heat release calculated at step 215.Finally, at step 224, the ECU 12 adjusts engine control parameters tomeet a set point. For example, an IMEP target or the equivalent. In someinstances, at step 224, ECU 12 meets the set point by adjusting a setfuel substitution rate.

In some instances, high resolution triggering (up to 0.250 CAresolution) is provided from a low resolution encoder (e.g., a sensorreading a 60-2 tooth wheel), by using linear interpolation.

Optionally, and as discussed in more detail below, the ECU 12 can employa high efficiency processing method that enables processing of over 15combustion metrics per each cylinder for each cycle, while being fit ina standard “automotive” production ECU (with maximum allowable processorand memory). In particular, the vector of pressure readings from thecylinder pressure sensor is sampled at different resolutions based onwhere the cylinder is in the combustion cycle. Thus, the vector issampled at the highest resolution during only the most critical times,and the total amount of data processed is reduced. Also, the data iscollected and processed from the same memory for all cylinders.

In some instances, simultaneous control of a combustion phasing metric,for example centroid of heat release (CA50, a metric derived from highspeed processing of heat release rate for every cycle), is conductedwith actuation of combustion triggering phasing (e.g., spark advance ordiesel start of injection) concurrently with simultaneous control of acombustion energy metric (e.g., IMEP). This simultaneous control isachieved though actuation of total fuel quantity, either in-cylinder, ina diesel configuration, or extra-cylinder in, for example, in-portinjection of natural gas or gasoline.

In some instances, and as described in more detail below, a dual fuelmaximum substitution rate is calculated based on ratios of various heatrelease rate metrics, such as CA10, CA50, CA90, where all three metricsCA10, CA50 and CA90 are subsequently used to control the quantity offuel (fuel profile), and CA50, specifically, is used in controlling thephasing, i.e., the start of injection. Further CA10 can be used to as asurrogate control metric for start of combustion.

In some instances, real time processing of derived compression andexpansion polytropic coefficients from the pressure signals are used forhigh quality heat release rate calculations. The heat release ratecalculations include diagnostics of compression curve quality viacalculation of “motored” pressure curve. The heat release rate candiagnose changes in cylinder and pressure sensor quality via deviationsfrom the expected compression curve. In some instances, the polytropicconstants are recorded over time to determine a rate of drift ofpressure sensor or cylinder compressive quality due to ring and/or valvetightness.

In some instances, the system is configured to switch immediately andseamlessly from conventional diesel only to (i) “dual fuel” mode,whereby combustion starts shortly after trigger injection near TDC, or(ii) to “RCCI” mode, including early injection of a trigging mediumwhile maintaining both combustion phasing (e.g. SOC, CA50, LocPeak) andtotal combustion energy (IMEP) metrics.

In some instances, a pressure based knock index is calculated usingreal-time pressure trace smoothing and integrated, weighted, ripplecalculations. The knock index is fed to the control ECU for eithermaximum substitution or maximum spark advance limitations. Using theknock index, the system maintains operation on the edge of knock. Insome instances, the system monitors knock index and adjusts both airfuel ratio (AFR, Lambda) and spark timing for maximum efficiency at agiven NOx level. Can also include NOx sensor input. In some instances,the system uses the knock index to conduct real-time knock margincontrol by advancing the combustion phasing control variable (e.g. sparktiming) to a point where the knock intensity reaches a pre-set targetvalue and then the phasing control records this phasing angle, and thesystem then retards the timing to a preset ‘retard from knock’ value,thereby providing a best knock margin and efficiency balance. In someinstances, the system performs a statistical sample of the variation ofthe combustion phasing target relevant to the actual. A voting functionsubsequently checks the need to adjust spark timing, and, if the knockmargin, misfire, and efficiency meet goals, then a discrete change inspark timing is executed. Once the change is made, the value is heldconstant until another legitimized change is affected.

In some instances, the system calculates individual peak pressure errorfrom the mean peak pressure magnitude to achieve a cylinder injectedenergy balance by subsequently adding or subtracting energy forcylinders below or above the average, respectively.

In some instances, a rate of pressure rise is calculated. The magnitudeof the pressure and the rate of pressure rise are used to limit fuelenergy injection content or combustion phasing. In some instances, indual fuel engines, rate of pressure rise is used as a final protection,while the rate of heat release used as the primary control parameter. InRCCI, combustion phasing is first controlled via diesel injection timingand then rate of pressure rise is the key protection and controlparameter to control the ratio of the two fuels.

In some instances, the system computes combustion stability (COV ofIMEP) and uses this stability calculation to determine a lean misfireair-fuel-ratio. Once lean misfire AFR is known, air fuel ratiocontroller is set to keep charge richer than misfire limit by a givenmargin and combustion phasing control is used to maintain bestefficiency or input a NOx signal to retard timing to maintain NOx belowits limit.

In some instances, the system performs real-time calculation of fuelquality via real-time IMEP calculation. The IMEP is divided by injectedfuel mass quantity to calculate fuel specific energy content, Q. In someinstances, the calculation requires CA50 control to avoid confusion ofenergy and phasing. Once fuel quality is known, appropriate AFR andcombustion phasing control is executed.

In some instances, the system adapts to changing gas quality duringengine operation, without the need for a gas quality sensor, by usingthe combustion feedback instead.

Pressure Based Fuel Flex Gas Engine Controller

Typical gas engines today, for example natural gas engines, are operatedwith fixed spark timing along with an in-factory calibration for AFR.This typical configuration may provide a good knock margin and meetemissions norms on a firing engine put into operation. However, for someengines, the spark timing and AFR are set such that the center ofcombustion or CA50 (time of 50% fuel burn) are maintained in arelatively retarded location between 15° and 20° ATDC. These settingsare considered conservative and are set such that the worst envisionedfuel gas quality would not lead to engine damaging knock. In this typeof calibration, a provided knock sensor is utilized only in extremeconditions; otherwise, the knock signature is relatively low. The resultof this configuration is that while meeting NOx emissions norms, enginesrunning with ‘good fuel’ (i.e., having low knock tendency by virtue of ahigh methane number (MN)) are running with a less-than-optimal fuelconsumption during most or all of the time they are in operation. Thisloss of potential fuel economy can be, for example, as high as 1-4%.

In contrast, some engines use a more aggressive strategy wherein theknock sensor is used more intentionally for combustion phasing control.The assumption is that advancing combustion phasing to the point oflight knock gives the best fuel efficiency. This is especially true withJ-gap spark plugs, which have high cycle-to-cycle variation. In thesesystems, if the fuel quality changes with a drop in MN, there is timefor the knock to register in the controller and appropriate spark timingor AFR lean can be achieved to accommodate. This strategy depends uponthe knock sensor working. Additionally, when going to better ignitionmethods such as prechamber spark plugs and fuel fed pre-chambers, wherethe cycle to cycle variation is smaller and the combustion rate faster,that the condition of “light knock” would be overly advanced combustionand would be less efficient.

Additionally, there is no method in the aforementioned twoconfigurations to keep cylinder pressure below the mechanical limits orkeep the rate of pressure rise rate below the mechanical limit.Additionally, when fuel quality or AFR goes in the opposite direction,that is, leading toward poor combustion and misfire, typically the onlymethod of detection on existing engines is by monitoring cylinderexhaust port temperatures. However, this leads to an ambiguous monitoredcondition, as high temperatures indicated late combustion while very lowtemperatures indicate misfire. Misfire is also indicated byinstantaneous shaft speed variations, which can be used to corroborate alow temperature reading as a diagnostic of misfire.

One problem with the above systems is maintaining the engine between theknock limit and the misfire lift while maintain the NOx norms andachieving highest efficiency, especially when fuel quality changes andwhen the atmospheric conditions change. This problem is especiallychallenging when NOx norms are for very low NOx such as 1 TaLuft as lowas 0.5 or 0.25 or even 0.1 TaLuft where air. The systems detailed belowaddress the problem by using real-time in-cylinder combustion metrics toadjust both the combustion phasing and the burn duration to remainoptimal under the influence of changes in fuel and atmosphericconditions.

FIG. 3 is a schematic of an engine control unit 300 showing inputs 301to 305, outputs 341 to 343, and set points 331 to 333. The ECU 300 couldbe the same ECU 12 as shown in FIGS. 1 and 2, or it could anotherembodiment. The ECU 300 inputs data from a shaft encoder 301 (e.g., acrank angle sensor), an in-cylinder pressure sensor 302, a manifoldpressure sensor 303, a manifold temperature sensor 304, and an enginepower sensor 305. The ECU 300 also accepts a load set point 331, a CA50set point 332, and a NOx set point 333. The ECU 300 controls the engine(not shown) by outputting one or more of a throttle position signal 342,a spark advance signal 342, and a fuel rate signal 334.

FIG. 4 is a schematic of the internal processing steps 311-5, 321-3 ofthe engine control unit 300 of FIG. 3. The ECU 300, for each cylinderexecutes the following steps. First, in the pressure processing module21, at step 211, all constants, including vectors via engine geometry,are defined. Next, at step 212, the in-cylinder pressure is captured ata high resolution. In some instances, the pressure sensor is captured ata first (high) frequency during critical crank angles or combustionevents, and at a second (lower) or third (medium) frequency atnon-critical crank angles or combustion events. This pressure samplingwindow, shown in more detail in FIG. 5, enables the ECU to moreefficiently using existing memory and processing bandwidth to prioritizethe subsequent calculations to capture the critical combustion events.The per-cylinder pressure step 215, the heat release rates and burnmetrics are calculated. The pressure processing module 21 can calculatethe IMEP at step 316, and the engine indicated efficient and brakeefficiency can be calculated at step 317.

Finally, the engine control module 22 of the ECU 300 is configured witha first module 321 adjusting the throttle position 341 to maintain anair fuel ratio 321, a second module 322 adjusting a spark advance 342 tomaintain CA50 at the CA50 set point 332, and a third module 323adjusting the fuel rate 323 to maintain the engine load at the engineload set point 331.

Referring to FIG. 3 and FIG. 4, by taking directly into the ECU 300 theengine power 305, MAP 303, and MAT 304, shaft encoder 301 and cylinderpressure 302 signals for each cylinder directly, and processing them atsteps 311-313 to determine internally key combustion metrics such asCA50 (center of combustion), 10-90% burn duration, and IMEP, the systemuses calibrated values for these metrics and then determines and adjuststhe proper spark advance 342, throttle position 341, and fuel flow rateto maintain engine power and NOx emissions targets, and best operatingpoint efficiency while protecting the engine from knock, misfire, andover pressure—without any of the following sensors: knock sensors,lambda/O2 sensor, exhaust port temperature sensors.

Aspects represent a significant improvement, because by using pressuresensors instead of knock, lambda, and exhaust temp sensors, engineprotection is improved, sensor count goes down, NOx compliance isimproved (especially at low NOx points), and efficiency is maximized.The improvements are possible due to the ECU having built in cylinderpressures processing and ability to generate in real time combustionmetrics such as heat release rate and the offshoots of these CA50 and10-90 burn duration.

Variable Pressure Sampling Windows

FIG. 5 is a graph 500 of pressure vs. crank angle for a cylinder showingthree pressure sampling rate windows 501 a,b,c. The sampling ratewindows 501 a,b,c represent regions where the ECU samples the pressuresensor 302 at different sampling rates corresponding to the combustionevents taking placing in the windows 501 a,b,c. In FIG. 5, a pressuretraces 502, 503 are shown for a complete combustion event in a cylinder,e.g., 720° total, with 0° representing top-dead-center. Pressure trace502 represents a pressure rise from combustion in the cylinder over andabove the trace 503, which represents the pressure from compression viathe piston. The pressures trace 502 represents the raw in-cylinderpressure sensor 302 output. The graph 500 is divided into five windows501 a through 501 c during which the pressure sensor is sampled atdifferent rates by the ECU 300. A first sampling window 501 a representsthe pressures of least concern to the ECU 300 for efficientlycontrolling the engine, as there is not much, operationally speaking,occurring in these windows. Thus, the pressure may be sampled at thelowest rate in this window. In certain instances, the sampling rate is 2to 8 crank angle degrees per sample (i.e., one pressure sample every 2to 8 degrees rotation of the crank). The first window 501 a spans thecrank angles 180° before and 180° after top-dead-center, but in otherinstances, could span fewer or more crank angles. Likewise, a higher orlower sampling rate could be employed in the first window.

A second sampling window 501 b spans the crank angles+/−180° to +/−60°with respect to top-dead-center. The pressure signals in the secondwindow 501 b represent pressures of intermediate concern to the ECU 300in operation of the engine, as the pressure change in these windows ismore operationally significant. Thus, the pressure 502 in the secondwindow 501 b may be sampled at a higher rate than during the firstwindow 501 a. In certain instances, the sampling rate in the secondwindow is 1 to 6 crank angle degrees per sample. As above, the secondwindows 501 b could span fewer or more crank angle degrees, and higheror lower sampling rates than 1 to 6 crank angle degrees per sample couldbe employed.

Finally, a third window 501 c spans the remainder (180° in this example)and is centered on the top-dead-center position of the piston andrepresents the location of pressure signal locations critical to theECU's 300 calculations of combustion metrics 313 and subsequent control341-3 of the engine. In addition to the third window 501 c encompassingTDC, the window is also when the ignition event occurs (e.g., sparkevent in a spark fired engine). Accordingly, the pressure 502 is sampledin the third window 501 c at the highest rates, higher than in the firstor second windows. In certain instances, the sampling rate in the thirdwindow is 0.25 to 0.5 degrees per sample (i.e., 2 to 4 samples per crankangle). Again, as above, the third window could span few or more crankangles and the sampling rate could be higher or lower than the example.

In some instances, the span of windows 501 a to 501 c are selected basedon the combustion conditions and the engine cycle, and may be, forexample represent pressure sampling rates variably determined by the ECUduring operation of the engine.

In some instances, fewer or more than three pressure sampling windows501 a,b,c are used, and, in some instances, the windows 501 a,b,c areselected based on computer models of the combustion and subsequentlyverified with physical tests.

The ECU's 300 use of pressure sampling windows 501 a,b,c enables the ECUto allocate memory and computation resources to calculating thecombustion metrics during the pressure signal locations of highestimportance to the effective control of the engine based. Specifically,in some instances, the ECU 300 operates the pressure sampling widows 501a,b,c at a sampling level, that is, the ECU only captures data from thepressure sensor 302 at the rates determined by the window 501 a,b,c,thereby further saving resources by not having to drop captured data inorder to comply with parameters of the sampling windows 501 a,b,c.

In some instances, the pressure sampling rate in the windows 501 a,b,cis variable and the windows represent a rate-change of the pressuresampling rate.

Acronyms/Abbreviations

ATDC=after top dead center

BTDC=before top dead center

CA50=location of 50% mass fraction burn (crank angle degrees ATDC)

CAN=controller area network

COV=coefficient of variation

ECU=engine control unit

EGR=exhaust gas recirculation

HCCI=homogeneous charge compression ignition

IMEP=indicated mean effective pressure (bar)

IVC=intake valve closing angle

LTC=low temperature combustion

MAP=manifold absolute pressure (bar)

MAT=manifold absolute temperature (K)

NOx=oxides of nitrogen

PCCI=premixed charge compression ignition

Ploc=location of peak pressure (crank angle degrees ATDC)

Pmax=maximum cylinder pressure (bar)

R&D=research and development

RCCI=reactivity controlled compression ignition

RPR=rate of pressure rise (bar/crank angle degree)

RT-CDC=real-time combustion diagnostics and control

SOC=start of combustion (crank angle degrees ATDC)

An example apparatus for controlling operation of an internal combustionengine includes an in-cylinder pressure sensor configured to measurepressure in a cylinder of the engine and generate a correspondingpressure signal, a crank angle sensor configured to measure the crankangle of the engine and generate a corresponding crank angle signal andan engine control unit capable to couple the pressure sensor and thecrank angle sensor. The engine control unit is configured to: (a) samplethe pressure signal and the crank angle signal at a specified frequency,the specified frequency in a first range of the crank angle thatincludes a piston top-dead-center being greater than the specifiedfrequency in a second range of the crank angle, (b) calculate acombustion metric indicative of the combustion occurring in the cylinderas a function of the pressure signal and the crank angle signal, and (c)determine fuel input signal, throttle position signal, and an ignitiontiming signal for the engine based on the combustion metric.

In some examples, the specified frequency in the first range is between0.25° and 0.50° crank angle per sample.

In some examples, the second range includes the bottom-dead-centerposition, and wherein the specified frequency in the second range isbetween 2.0° and 8.0° crank angle per sample.

In some examples, the apparatus further includes a third range betweenthe first and second ranges, and wherein the specified frequency in thethird range is between 1.0° and 6.0° crank angle per sample.

In some examples, the first range coincides with the crank angle of theignition timing signal.

In some examples, combustion metric comprises at least one of anadiabatic heat release rate of combustion in the cylinder, a maximumpressure in the cylinder, the crank angle location of the maximumpressure in the cylinder, a crank angle location of each of the 10%, 50%and 90% combustion (i.e., burn) conditions, a 10%-90% combustionduration, or indicated mean effective pressure (IMEP) for each cylinder.

In some examples, ECU receives one or more of the following set points:engine load set point, CA50 set points, and NOx set point, and whereinthe ECU is further configured to determine the throttle position signalas a function of the combustion metric and one of the set points,determine the ignition timing signal as a function of the combustionmetric and one of the set points, and determine the fuel input signal asa function of the combustion metric and one of the set points.

Another example is a method of controlling an internal combustionengine. The method comprises, sampling a crank angle sensor of theengine. Sampling a pressure sensor of each cylinder of the engine at afirst frequency during a first range of cylinder crank angles, the firstrange of cylinder crank angles including the ignition position of thecylinder. Sampling the pressure sensor at a second frequency during asecond range of cylinder crank angles, the second frequency being lowerthan the first frequency. Calculating a combustion metric based on thesampled crank angle and pressure. Determining an engine controlparameter, the engine parameter including at least one of an enginethrottle position, spark advance, and fuel-air ration based on thecalculated combustion metric. Controlling the engine based on the enginecontrol parameter.

In some examples, first frequency is between 0.25° and 0.50° of thecrank angle per sample of the pressure sensor.

In some examples, the second frequency is between 2.0° and 8.0° of thecrank angle per sample of the pressure sensor.

In some examples, the method further includes sampling the pressuresensor at a third frequency during a third range of cylinder crankangles, the third frequency being between the first and secondfrequencies and the third range being between the first and secondranges.

In some examples, the third frequency is between 1.0° and 6.0° of thecrank angle per sample of the pressure signal.

In some examples, the method further includes modifying the first rangebased on the sampled pressure.

In some examples, the method further includes modifying the first rangebased on the calculated combustion metric.

In some examples, determining the engine control parameter is based onone or more combustion metrics, where the one or more combustion metricsare calculated from only the pressure and crank angle sensors as sensorinputs.

In some examples, the combustion metric includes one or more of thefollowing: an adiabatic heat release rate of combustion in the cylinder,a maximum pressure in the cylinder, the crank angle location of themaximum pressure in the cylinder, a crank angle location of each of the10%, 50% and 90% burn conditions, a 10%90% combustion duration, orindicated mean effective pressure (IMEP) for each cylinder.

In some examples, the method further includes receiving one or more ofthe following set points: engine load set point, CA50 set points, andNOx set point, determining the throttle position signal as a function ofthe combustion metric and one of the set points, determining theignition timing signal as a function of the combustion metric and one ofthe set points, and determining the fuel input signal as a function ofthe combustion metric and one of the set points.

In some examples, the method further includes determining a knockquality of a cylinder combustion event based on the combustion metric.

In some examples, the engine is a dual fuel engine, the method furtherincludes determining a maximum safe substitution rate between a firstfuel and a second fuel, and controlling fuel substitution rate betweenthe first fuel and the second fuel based on the maximum safesubstitution rate.

In some examples, the method further includes controlling fuelsubstitution between the first fuel and the second fuel based on a CA50set point.

Aspects can include one or more of the following:

In some examples, the method or apparatus includes monitoring enginecylinder pressure.

In some examples, the method or apparatus includes inputting an enginecrank angle signal to an engine control unit.

In some examples, the method or apparatus includes combining cylinderpressure with engine crank angle and thus associate with the cylindervolume. In some examples, data is analyzed in time, and the dataincludes engine crank angle or engine cylinder volume.

In some examples, the method or apparatus analyzes the cylinder pressuresignal against time, crank angle (CA), or cylinder volume.

In some examples, the method or apparatus includes calculating keycombustion metrics. In some examples, the combustion metrics includeIMEP, CA50, and 10-90% burn duration.

In some examples, the method or apparatus includes a means to controlone or more of the following engine control parameters: spark advance,throttle position, and fuel flow rate. In some examples, the method orapparatus controls the above engine control parameters to achieve ormaintain one or more of a load set point and a NOx set point, either ofwhich may be controlled to achieve a best efficient at the set point.Additionally, in some examples, the method or apparatus controls theengine at the above set points without knock or misfire and withinacceptable NOx outputs. In some examples, the method or apparatus isconfigured to control the engine at the above set points over a widerange of fuel quality, for example, MN, QLHV.

Generally, one skilled in the art will appreciate that the devices andmethods described herein, in some configurations, eliminate need for MAFsensor, NOx sensor, Knock sensors, Port Ext Temp sensors. Additionally,the devices and methods described herein, in some configurations, avoidknock, detect and avoid misfire, maintain NOx within norms and achievebest engine efficiency. One skilled in the art will also appreciate thatthe devices and methods described herein adapt to variable fuel qualityas characterized by MN (methane number) and Energy Content (MBTU/m³).

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. Accordingly, otherembodiments are within the scope of the following claims.

1. An apparatus for controlling operation of an internal combustion engine, comprising: an in-cylinder pressure sensor configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal; a crank angle sensor configured to measure the crank angle of the engine and generate a corresponding crank angle signal; and an engine control unit couplable to the pressure sensor and the crank angle sensor, the engine control unit configured to: (a) sample the pressure signal and the crank angle signal at a specified frequency, the specified frequency in a first range of the crank angle that includes a piston top-dead-center being greater than the specified frequency in a second range of the crank angle, (b) calculate a combustion metric indicative of the combustion occurring in the cylinder as a function of the pressure signal and the crank angle signal, and (c) determine fuel input signal, throttle position signal, and an ignition timing signal for the engine based on the combustion metric.
 2. The apparatus of claim 1, wherein the specified frequency in the first range is between 0.25° and 0.50° crank angle per sample.
 3. The apparatus of claim 1, wherein the second range includes the bottom-dead-center position, and wherein the specified frequency in the second range is between 2.0° and 8.0° crank angle per sample.
 4. The apparatus of claim 1, further including a third range between the first and second ranges, and wherein the specified frequency in the third range is between 1.0° and 6.0° crank angle per sample.
 5. The apparatus of claim 1, wherein the first range coincides with the crank angle of the ignition timing signal.
 6. The apparatus of claim 1, wherein combustion metric comprises at least one of: an adiabatic heat release rate of combustion in the cylinder, a maximum pressure in the cylinder, the crank angle location of the maximum pressure in the cylinder, a crank angle location of each of the 10%, 50% and 90% burn conditions, a 10%90% combustion duration, or indicated mean effective pressure (IMEP) for each cylinder.
 7. The apparatus of claim 6, wherein the ECU receives one or more of the following set points: engine load set point, CA50 set points, and NOx set point, and wherein the ECU is further configured to: determine the throttle position signal as a function of the combustion metric and one of the set points, determine the ignition timing signal as a function of the combustion metric and one of the set points, and determine the fuel input signal as a function of the combustion metric and one of the set points. 8-20. (canceled)
 21. A controller for controlling operation of an internal combustion engine of an engine system, the engine system comprising a pressure sensor configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal and a crank angle sensor configured to measure the crank angle of the engine and generate a corresponding crank angle signal, the controller comprising: a processor couplable to the pressure sensor and the crank angle sensor; and at least one non-transitory computer readable medium storing instructions operable to cause the processor of the controller to perform operations comprising: (a) sample the pressure signal and the crank angle signal at a specified frequency, the specified frequency in a first range of the crank angle that includes a piston top-dead-center being greater than the specified frequency in a second range of the crank angle, (b) calculate a combustion metric indicative of the combustion occurring in the cylinder as a function of the pressure signal and the crank angle signal, and (c) determine fuel input signal, throttle position signal, and an ignition timing signal for the engine based on the combustion metric.
 22. A controller for controlling operation of a dual-fuel internal combustion engine of an engine system, the engine system comprising a pressure sensor configured to measure pressure in a cylinder of the engine and generate a corresponding pressure signal and a crank angle sensor configured to measure the crank angle of the engine and generate a corresponding crank angle signal, the controller comprising: a processor couplable to the pressure sensor and the crank angle sensor; and at least one non-transitory computer readable medium storing instructions operable to cause the processor of the controller to perform operations comprising: (a) sample the crank angle signal, (b) sample the pressure signal of each cylinder of the engine at a first frequency during a first range of cylinder crank angles, the first range of cylinder crank angles including the ignition position of the cylinder and at least a portion of a combustion period of the cylinder, (c) sample the pressure signal at a second frequency during a second range of cylinder crank angles, the second frequency being lower than the first frequency, (d) calculate combustion metrics including IMEP, an adiabatic heat release rate of combustion in the cylinder, and combustion phasing based on the sampled crank angle and pressure signals, (e) determine a combustion phasing trigger and a substitution rate between a first fuel and a second fuel as a function of the calculated adiabatic heat release rate of combustion in the cylinder, (f) adjust the combustion phasing trigger based on the calculated combustion phasing to meet a combustion phasing target, (g) adjust the fuel substitution rate based on the calculated IMEP to meet an IMEP target, and (h) control the engine based on the adjusted combustion phasing trigger and fuel substitution rate.
 23. The controller of claim 22, wherein the adiabatic heat release rate of combustion in the cylinder is calculated from only the pressure and crank angle sensors as sensor inputs.
 24. The controller of claim 22, wherein the combustion metrics include one or more of the following: the adiabatic heat release rate of combustion in the cylinder, a maximum pressure in the cylinder, the crank angle location of the maximum pressure in the cylinder, a crank angle location of each of the 10%, 50% and 90% burn conditions, a 10%90% combustion duration, the IMEP for each cylinder, a rate of pressure rise, and a knock quality.
 25. The controller of claim 22, wherein the instructions include causing the processor to: determine a knock quality of a cylinder combustion event based on the calculated adiabatic heat release rate of combustion in the cylinder; determining a max safe substitution rate as a function of the knock quality; and adjusting the fuel substitution rate based on the max safe substitution rate.
 26. The controller of claim 22, wherein the instructions include causing the processor to simultaneously control the fuel substitution rate to meet the IMEP target and the combustion phasing trigger to meet the combustion phasing target by controlling a total fuel quantity.
 27. The controller of claim 22, wherein the combustion phasing target is a CA50 set point and wherein controlling the engine includes controlling the engine to maintain the CA50 setpoint.
 28. The controller of claim 22, wherein the instructions include causing the processor to maintain a maximum substitution rate by adjusting the fuel substitution based on the max safe substitution rate while adjusting the combustion phasing trigger to maintain the knock quality below target knock margin.
 29. The controller of claim 22, wherein the instructions include causing the processor to modify the first range based on the sampled pressure.
 30. The controller of claim 22, wherein the instructions include causing the processor to modify the first range based on the calculated combustion metrics. 